soc/amd/common/psp_gen2: use MMIO access again

Now that we have a get_psp_mmio_base function that will work on all SoCs
that use the psp_gen2 code, we can move back to accessing the PSP
registers via their MMIO mapping. This sort-of reverts
commit 198cc26e4951 ("soc/amd/common/block/psp/psp_gen2: use SMN access
to PSP").

When doing SMN accesses from the SMI handler after the OS has taken over
ownership of the platform, there's the possibility to cause trouble by
clobbering the SMN access index register from SMM. So that should be
either avoided completely or the SMI code needs to save and restore the
original contents of the SMN index register.

The PSP MMIO base will be set up by the FSP before the resource
allocation in coreboot and be treated like a fixed resource by the
allocator. The first SMI where corresponding handler calls
'get_psp_mmio_base' happens when ramstage triggers the APM_CNT_SMMINFO
SMI right after mpinit which happens after the resource allocation. So
the PSP MMIO base address is expected to be configured and so the
'get_psp_mmio_base' function will cache the base address and won't need
to do any SMN access in subsequent calls that might happen after the OS
has take over control.

This isn't currently an issue, since the only PSP mailbox command from
the SMI handler after coreboot is done and the OS has taken over will
be during the S3/S4/S5 entry, and this will be triggered by the OS as
the last step after it is done with all its preparations for suspend/
shutdown.  There will however be future patches that add SMI-handlers
which can send PSP mailbox commands during OS runtime, and so we have
to make sure we don't clobber the SMN index register.

TEST=PSP mailbox commands are still sent correctly on Mandolin.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I25f16d575991021d65b7b578956d9f90bfd15f6c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83448
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

0 files changed, 0 insertions, 0 deletions